Image forming apparatus and image processing apparatus

ABSTRACT

In a case where another first region exists which faces the edge pixel across a second region on a line in a predetermined direction passing through the edge pixel of the first region, the correcting unit selects a correction amount for correcting the exposure amount applied by the exposing unit for the pixel to be corrected from information describing a plurality of correction amounts in accordance with a first number of pixels being a number of pixels on the line within the second region between the first region and the other first region and corrects the exposure amount for the pixel to be corrected in accordance with the selected correction amount.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.15/344,331, filed Nov. 4, 2016, which claims priority from JapanesePatent Application No. 2015-219795, filed Nov. 9, 2015, which are herebyincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

One disclosed aspect of the embodiments relates to a technology forreducing a consumed amount of a developing agent in an image formingapparatus.

Description of the Related Art

In an image forming apparatus, reduction of a consumed amount of tonerbeing a developing agent has been demanded. Japanese Patent Laid-OpenNo. 2004-299239 discloses a configuration which reduces the exposureintensity for an image having some area to reduce the consumed amount oftoner. In an image forming apparatus, a phenomenon called “sweep-up” mayoccur which is an increased amount of toner adhered to an edge region ona rear end side in a rotational direction of a photosensitive member ofan electrostatic latent image formed on the photosensitive member.Japanese Patent Laid-Open No. 2007-272153 discloses a configurationwhich suppresses an influence caused by sweep-up. More specifically, acorrection region is determined based on a data value of a pixel ofinterest and data values of pixels positioned on a downstream side by apredetermined amount in a sub scanning direction with respect to thepixel of interest. A pixel positioned on an upstream side by apredetermined amount in the sub scanning direction of the pixel in thecorrection region is further defined as a correction region and theexposure amount in the pixel in the correction region is adjusted tosuppress an influence caused by the sweep-up. Such suppression of theinfluence of the sweep-up can reduce the consumed amount of toner.Additionally, in an image forming apparatus, a phenomenon called an“edge effect” may occur which is an increased amount of toner adhered toan edge region of an electrostatic latent image formed on aphotosensitive member.

Because the strength of such sweep-up and edge effects at an edge mayvary in accordance with another image in vicinity of the edge, the imagequality may be deteriorated even with the configurations disclosed inJapanese Patent Laid-Open Nos. 2004-299239 and 2007-272153.

One disclosed aspect of the embodiments provides an image formingapparatus and an image processing apparatus, which can reduce theconsumed amount of a developing agent while preventing reduction ofimage quality.

SUMMARY OF THE INVENTION

An aspect of the embodiments provides an image forming apparatus formingan image on basis of image data. The apparatus includes a photosensitivemember, an exposing unit configured to expose the photosensitive memberto light to form an electrostatic latent image, a developing unitconfigured to develop the electrostatic latent image on thephotosensitive member by using a developing agent to form an image, adiscriminating unit configured to, on basis of the image data,discriminate a first region being a region having a series of pixelswith a pixel value equal to or higher than a predetermined value and asecond region being a region having a series of pixels with a pixelvalue lower than the predetermined value, an identifying unit configuredto identify a pixel to be corrected from the pixels within the firstregion on basis of identification information describing a relationshipbetween an edge pixel positioned at an edge of the first region and thepixel to be corrected, and a correcting unit configured to correct anexposure amount applied by the exposing unit for the pixel to becorrected from an exposure amount described in the image data, wherein,in a case where another first region exists which faces the edge pixelacross a second region on a line in a predetermined direction passingthrough the edge pixel of the first region, the correcting unit selectsa correction amount for correcting the exposure amount applied by theexposing unit for the pixel to be corrected from information describinga plurality of correction amounts in accordance with a first number ofpixels being a number of pixels on the line within the second regionbetween the first region and the other first region and corrects theexposure amount for the pixel to be corrected in accordance with theselected correction amount.

Further features of the disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an image forming apparatusaccording to an embodiment.

FIGS. 2A and 2B are explanatory diagrams of a developing methodaccording to an embodiment.

FIG. 3 is an explanatory diagram for a principle of occurrence of anedge effect.

FIGS. 4A and 4B illustrate images having an edge effect and a sweep-up.

FIGS. 5A to 5C are explanatory diagrams illustrating a principle ofoccurrence of a sweep-up.

FIG. 6 illustrates a configuration of control over an exposure amountaccording to an embodiment.

FIGS. 7A to 7D are explanatory diagrams illustrating a method forcontrolling an exposure amount according to an embodiment.

FIG. 8 is a functional block diagram illustrating a CPU for controllingan exposure amount according to an embodiment.

FIGS. 9A and 9B illustrate image s according to an embodiment.

FIGS. 10A to 10D illustrate heights of toner of toner images subject toan edge effect according to an embodiment.

FIGS. 11A to 11E illustrate pixels to be corrected against an edgeeffect according to an embodiment.

FIGS. 12A to 12D are explanatory diagrams illustrating correctionsagainst an edge effect according to an embodiment.

FIGS. 13A and 13B illustrate exposure-amount adjustment parametersaccording to an embodiment.

FIGS. 14A and 14B illustrate pixel exposure methods according to anembodiment.

FIG. 15 illustrates images according to an embodiment.

FIGS. 16A and 16B illustrate heights of toner of toner images subject toa sweep-up according to an embodiment.

FIGS. 17A and 17B illustrate pixels to be corrected against a sweep-upaccording to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

Illustrative embodiments will be described below with reference todrawings. The following embodiments are given for illustration purposeand are not intended to limit details of embodiments. Components thatare not necessary for describing embodiments are not illustrated indrawings.

First Embodiment

FIG. 1 is a configuration diagram illustrating an image formingapparatus 101 according to this embodiment. A photosensitive member 1being an image bearing member is driven to rotate in a directionindicated by an illustrated arrow for image formation. A charging unit 2electrostatically charges a surface of the photosensitive member 1 to aneven electric potential. An exposing unit 7 exposes theelectrostatically charged surface of the photosensitive member 1 tolight based on image data for forming an electrostatic latent image onthe photosensitive member 1. The exposing unit 7 is driven in responseto a drive signal 71 output from an image calculating unit 9. Anexposure control unit 19 in the image calculating unit 9 adjusts suchthat the exposure intensity achieved by the exposing unit 7 with voltageVa can be equal to a target value.

A developing unit 3 includes a container 13 configured to store tonerbeing a developing agent and a developing roller 14. The toner may benonmagnetic single-component toner, two-component toner, or magnetictoner. A regulating blade 15 is provided which is configured to regulatethe layer thickness of toner supplied to the developing roller 14 to apredetermined value. The regulating blade 15 may be configured to giveelectric carriers to toner. The toner is conveyed by a developing roller14 to a development region 16. The development region 16 refers to aregion where the developing roller 14 and the photosensitive member 1are in proximity to or in contact with each other for adhering toner toan electrostatic latent image. The developing unit 3 adheres toner anelectrostatic latent image formed on the photosensitive member 1 tovisualize it as a toner image. A transfer printing unit 4 performstransfer printing the toner image formed on the photosensitive member 1formed on a recording material P. A fixing unit 6 applies heat andpressure to the recording material P to fix, to the recording materialP, the toner image having undergone transfer printing to the recordingmaterial P.

The CPU 10 in the image calculating unit 9 is a control unit configuredto generally control over the image forming apparatus 101. According toan embodiment, the overall control, which will be described below, maynot be performed by the CPU 10, but a part thereof may be performed byan ASIC 18. Alternatively, the overall control, which will be describedbelow, may be performed by the ASIC 18. A memory 11 is a storage unitconfigured to store image data and hold an LUT 112. The LUT 112 is alookup table containing correction width parameters and exposure-amountadjustment parameters. The image calculating unit 9 receives image datatransmitted from a host computer 8, suppresses influence of an edgeeffect and a sweep-up on basis of the correction width parameters andexposure-amount adjustment parameters held in the LUT 112, and correctsthe image data to reduce the toner consumed amount.

Next, a development system in the developing unit 3 will be describedwith reference to FIGS. 2A and 2B. FIG. 2A illustrates a configurationof a jumping development system. According to the jumping developmentsystem, the developing roller 14 and the photosensitive member 1 are notin contact with each other, but a gap 17 having a predetermined distanceis provided therebetween. An AC bias on which a direct current bias issuperimposed is used as a developing bias to be output from thedeveloping roller 14. FIG. 2B illustrates a configuration of a contactdevelopment system. According to the contact development system, thedeveloping roller 14 and the photosensitive member 1 are in contact witheach other. A direct current bias is used as a developing bias to beoutput from the developing roller 14. In the contact development system,the photosensitive member 1 and the developing roller 14 may beconfigured to rotate in rotational directions reverse to each other, asillustrated in FIG. 2B, that is, such that their surfaces can move inone direction in the development region 16.

Next, a principle of occurrence of an edge effect and a sweep-up in anedge part where an increased amount of toner is adhered to anelectrostatic latent image will be described. The edge effect hererefers to a phenomenon that an intensified electric field on anelectrostatic latent image formed on the photosensitive member 1, thatis, at a boundary between an exposed region and the other unexposedregion causes toner to be excessively adhered to an edge of theelectrostatic latent image. It is assumed here, for example, that animage to be formed has a uniform density. As illustrated in FIG. 3,electric lines of force from the unexposed regions 301 and 302surrounding the exposed region 300 go round the edges of the exposedregion 300 so that the intensity of the electric fields in the electricfields can be higher than the other part of exposed region 300. Thus,more toner may be adhered to the edges of the exposed region 300compared to the other part.

FIG. 4A illustrates a toner image 400 having an edge effect. FIG. 4Aillustrates an arrow A indicating a conveying direction of a tonerimage, that is, the rotational direction of the photosensitive member 1.The image data on which the toner image 400 is based have equal pixelvalues as a whole, that is, the toner image 400 has a uniform density.In a case where an edge effect occurs thereon, toner is intensivelyadhered to a whole edge region 402 a of the toner image 400. As aresult, the edge region 402 a has a density higher than the density of anon-edge region 401 a. Such an edge effect generally occurs when thejumping development system is applied in which a gap is provided betweenthe photosensitive member 1 and the developing roller 14.

On the other hand, the sweep-up refers to a phenomenon that tonerconcentrates on an edge region on a rear end side in the rotationaldirection of the photosensitive member 1 of a toner image. According tothe contact development system, the peripheral speed of the developingroller 14 is higher than the peripheral speed of the photosensitivemember 1 so that the thickness of the toner on the photosensitive member1 can be equal to a predetermined value. In the development region 16,as illustrated in FIG. 5A to FIG. 5C, an electrostatic latent image isdeveloped with toner conveyed by the developing roller 14. FIGS. 5A to5C illustrate circles indicating toner. Because the developing roller 14rotates at a speed higher than that of the photosensitive member 1,their positional relationship on the surface continuously changes. Asillustrated in FIG. 5A, when a rear end of an electrostatic latent image600 enters to the development region 16, the toner on the developingroller 14 positions more closely to the rear side in the rotationaldirection with respect to the starting position of the developmentregion 16. However, because the developing roller 14 rotates at a speedhigher than the rotating speed of the photosensitive member 1, the toneron the developing roller 14 gets ahead of the rear end of theelectrostatic latent image 600 while the rear end of the electrostaticlatent image 600 passes through the development region 16 as illustratedin FIG. 5B. Because the toner on the developing roller 14 is supplied tothe rear end of the electrostatic latent image 600 as illustrated inFIG. 5C, the amount of toner to be adhered to the rear end of theelectrostatic latent image increases. This is a mechanism of occurrenceof the sweep-up.

FIG. 4B illustrates a toner image 410 having a sweep-up. FIG. 4Billustrates an arrow A indicating a conveying direction of a tonerimage, that is, a rotational direction of the photosensitive member 1.The image data on which the toner image 410 is based have equal pixelvalues as a whole, that is, the toner image 410 has a uniform density.In a case where a sweep-up occurs, toner is intensively adhered to arear end region 402 b of the toner image 410. As a result, the rear endregion 402 b has a density higher than the density of the other region401 b.

FIG. 6 illustrates a control configuration of the exposing unit 7. Theexposure control unit 19 has an IC 2003 including an 8-bit DA converter(DAC) 2021 and a regulator (REG) 2022. The IC 2003 adjusts voltage VrefHoutput from the regulator 2022 on basis of an intensity adjustmentsignal 73 set by the CPU 10. The voltage VrefH is a reference voltagefor the DA converter 2021. The IC 2003 sets input data 2020 for the DAconverter 2021 so that the DA converter 2021 outputs a voltage Va to theexposing unit 7. A VI conversion circuit 2306 in the exposing unit 7converts the voltage Va to an electric current value Id and outputs itto a driver IC 2009. The driver IC 2009 controls the exposure intensityof the exposing unit 7 on basis of the electric current value Id. Inother words, the exposure control unit 19 can control the exposureintensity of the exposing unit 7 on basis of the voltage Va. The driverIC 2009 further turns a switch (SW) for the driver IC 2009 in accordancewith a drive signal 71 output from the image calculating unit 9. The SWis turned to select whether electric current IL is to be fed to a laserdiode (LD) of the exposing unit 7 or to a dummy resistance R1 for ON/OFFcontrol over the light emission to be performed by the LD.

Next, a method for controlling the exposure amount of a pixel will bedescribed. FIG. 7A illustrates a state acquired by exposing a wholeregion of one pixel to light with 100% intensity of a predeterminedtarget intensity. FIGS. 7B to 7D illustrate pixels having asubstantially half density of that of the pixel in FIG. 7A. The pixel inFIG. 7B has a state acquired by exposing a whole region of one pixel tolight with 50% intensity of the predetermined target intensity. Theexposure intensity here is controlled with voltage Va output from theexposure control unit 19 to the exposing unit 7, as described withreference to FIG. 6. FIGS. 7C and 7D illustrate states of one pixeldivided into N sub pixels (where N is a natural number equal to orhigher than 2) acquired by exposing the sub pixels to light with 100%intensity of the predetermined target intensity. This may be achieved bysetting voltage Va such that the exposure intensity can be equal to atarget intensity and turning on/off the SW in response to the drivesignal 71 in the control configuration in FIG. 6. In this case, thedrive signal 71 is a PWM (pulse width modulation) signal.

FIG. 8 illustrates functional blocks in the CPU 10 for suppressing anedge effect. According to this embodiment, the CPU 10 is configured toperform processing for suppressing an edge effect. However, as alreadydescribed above, the processing may be performed in cooperation with theASIC 18 or by the ASIC 18 alone. The parameter setting unit 902 notifiesand sets a correction width parameter on the LUT 112 to and in the imageanalyzing unit 901. The parameter setting unit 902 notifies and sets anexposure-amount adjustment parameter on the LUT 112 to and in theexposure amount adjusting unit 903. The image data 904 transmitted fromthe host computer 8, that is, input image data, are stored in the memory11 illustrated in FIG. 1. The image analyzing unit 901 identifies apixel at which an edge effect may possibly occur from pixels of an imageformed from the image data 904 on basis of the correction widthparameter and notifies the identified pixel to the exposure amountadjusting unit 903. The exposure amount adjusting unit 903 corrects thepixel value of the pixel identified by the image analyzing unit 901 onbasis of the exposure-amount adjustment parameter to generate correctedimage data. The exposing unit 7 is controlled on basis of the correctedimage data, that is, the output image data.

The correction width parameter is identification information by which apixel having an edge effect can be identified and, according to thisembodiment, is information describing a range of pixels at which an edgeeffect may possibly occur by using a distance from a pixel at an edgeor, in this example, the number of pixels from the edge. In other words,the identification information is information describing a relationshipbetween an edge pixel positioned at an edge and a pixel to be corrected.For example, when the correction width parameter is “5”, it isdetermined that an edge effect may occur at the five pixels from anedge. According to this embodiment, a pixel to be corrected is notidentified in a direction of a width having a number of pixels lowerthan a value of the correction width parameter. The correction widthparameters and the exposure-amount adjustment parameters are acquired inadvance through experiments and simulations. Methods which adjust anexposure amount of a pixel may include, as illustrated in FIGS. 7B, 7C,and 7D, a method which adjusts the exposure intensity and a method whichchanges the number of sub pixels to be exposed in response to a PWMsignal without changing the exposure intensity. Alternatively, theexposure intensity may be changed, and the number of sub pixels to beexposed in response to a PWM signal may then be changed.

Next, processing will be described which is to be performed by the imageanalyzing unit 901 for suppressing an edge effect. Though an edge in amain scanning direction is only described below, the same is true for anedge in a direction orthogonal to the main scanning direction, that is,a sub scanning direction. The sub scanning direction corresponds to arotational direction of the photosensitive member. Hereinafter, thedownstream side of the rotational direction of the photosensitive memberwill be called a “front side”, and the upstream side will be called a“rear side”. The following descriptions assume that the correction widthparameter is “5”. FIGS. 9A and 9B exemplarily illustrate images formedfrom the image data 904. FIG. 9A illustrates an image having imageregions 1801 a to 1801 c, and FIG. 9B illustrates an image having imageregions 1802 a to 1802 c. The expression “one image region” here refersto a region having a series of pixels to which toner is adhered. FIGS.9A and 9B assume that the widths in the sub scanning direction of theimage regions 1801 a to 1801 c and the image regions 1802 a to 1802 care equal to 10 pixels. Referring to FIG. 9A, an interval d1 in the subscanning direction between three image regions is larger than 10 pixelsequal to two times of a range of pixels at which an edge effect mayoccur, such as 11 pixels or larger. On the other hand, referring to FIG.9B, an interval d2 in the sub scanning direction between three imageregions is equal to or smaller than 10 pixels equal to two times of therange of pixels at which an edge effect may occur, such as five pixels.

In the image regions 1801 a to 1801 c, an edge in the main scanningdirection (or an edge in the horizontal direction in FIGS. 9A and 9B,which will simply be called an “edge”) has a sufficient margin on therear side or the front side so that a sufficient toner amount may besupplied for an edge effect. In other words, the image regions 1801 a to1801 c may have an edge effect at five or fewer pixels from the frontside and rear side edges. On the other hand, because the image region1802 a has a more sufficient margin at the downstream side edge than thefront side edge, an edge effect may occur at five or fewer pixels fromthe front side edge. On the other hand, the image region 1802 a has asmaller margin at the rear side edge close to the upstream side so thata weaker edge effect may occur due to an influence of the image region1802 b. Also, the front side and rear side edges of the image region1802 b have a weaker edge effect due to influences of the image region1802 a and 1802 c. Also, the front side edge of the image region 1802 chas a weaker edge effect due to an influence of the image region 1802 b.On the other hand, the rear side edge of the image region 1802 c has asubstantially equal edge effect to that of the image regions 1801 a to1801 c, that is, an edge effect stronger than that of the front side ofthe image region 1802 c.

FIG. 10A illustrates a height of toner adhered to the image regions 1801a to 1801 c. The positions of pixels in FIG. 10A are numbered from “1”in order from the front side in the sub scanning direction. The heightof pixels without an edge effect is normalized as “1”. As illustrated inFIG. 10A, the image regions 1801 a to 1801 c have an edge effectsubstantially equal to that of five or fewer pixels from the front sideand the rear side.

On the other hand, FIGS. 10B to 10D illustrate heights of toner adheredto the image regions 1802 a to 1802 c. FIGS. 10B to 10D are illustratedin the same manner as that in FIG. 10A. As illustrated in FIG. 10B, inthe sub scanning direction, five or fewer pixels from the front sideedge of the image region 1802 a have an edge effect substantially equalto that of the image regions 1801 a to 1801 c. However, the edge effectat the rear side edge of the image region 1802 a is weaker than the edgeeffect at the front side edge. As illustrated in FIG. 10C, the edgeeffect at the front side and rear side edges of the image region 1802 bis weaker than the edge effect of the image regions 1801 a to 1801 c.Furthermore, as illustrated in FIG. 10D, the rear side edge of the imageregion 1802 c has an edge effect substantially equal to that of theimage regions 1801 a to 1801 c while the front side edge of the imageregion 1802 c has a weaker edge effect.

As illustrated in FIG. 11A, all pixels in the image regions 1801 a to1801 c and 1802 a to 1802 c are assumed to have a pixel value “255”.FIGS. 11A to 11E illustrate pixels in an extracted center area in themain scanning direction of the image regions 1801 a to 1801 c and 1802 ato 1802 c. A pixel value between the image regions is assumed to be “0”.FIGS. 11A to 11E further illustrate arrows A each indicating the subscanning direction. FIG. 11B illustrates pixels identified by the imageanalyzing unit 901 as pixels to be corrected in the image regions 1801 ato 1801 c. Referring to FIGS. 11A to 11E, numbers 1 through 5 indicatedistances (lowest values) from an edge in the sub scanning direction.Because the correction width parameter is “5”, the image analyzing unit901 determines that an edge effect may possibly occur in ranges of fivepixels from the front side and rear side edges of the image regions 1801a to 1801 c. FIG. 11C illustrates pixels identified by the imageanalyzing unit 901 as pixels to be corrected in the image region 1802 a.Because the correction width parameter is “5”, the pixels to becorrected are identified in the same manner as that in the image regions1801 a to 1801 c illustrated in FIG. 11B. However, five or fewer pixelsfrom the rear side edge of the image region 1802 a have a weaker edgeeffect than the edge effect occurring in five or fewer pixels from thefront side edge as described above. Referring to FIG. 11C, a pixelhaving a weaker edge effect has “*” for distinction.

FIGS. 11D and 11E illustrate pixels identified by the image analyzingunit 901 as pixels to be corrected in the image region 1802 b and 1802c. A pixel having a weaker edge effect than the edge effect occurring inthe image region 1801 a, for example, has “*”, like FIG. 11C.

Next, correction of an exposure amount will be described. The occurrencelevel of an edge effect varies in accordance with the interval betweenimage regions, as illustrated in FIGS. 10A to 10D. From that, theadjustment amount for an exposure amount is changed on basis of theinterval between image regions. FIG. 12A illustrates a reduction ratioof the height of toner when the edge effect illustrated in FIG. 10Aoccurs. FIGS. 12B to 12D illustrate reduction ration of the heights oftoner when the edge effects illustrated in FIGS. 10B to 10D occur.

FIG. 13A illustrates exposure-amount adjustment parameters correspondingto pixels without “*” in FIGS. 11A to 11E. FIG. 13B illustratesexposure-amount adjustment parameters corresponding to pixels with “*”in FIGS. 11A to 11E. In other words, the exposure-amount adjustmentparameters illustrated in FIG. 13A are exposure-amount adjustmentparameter applied in a case where the number of serial pixels d(hereinafter, called an interval d) to which toner is not adheredbetween pixels of an edge of one image region and pixels at an edge ofanother image region is higher than a first threshold value. In a casewhere no other counter image region exists to one image region withpixels at edges of the one image and a margin, that is, pixels to whichtoner is not adhered therebetween, an exposure-amount adjustmentparameter in FIG. 13A is used irrespective of the number of pixels inthe margin.

On the other hand, the exposure-amount adjustment parameters illustratedin FIG. 13B are applied in a case where the interval d is equal to orlower than the first threshold value. The first threshold value is avalue two times a correction width parameter, for example. In otherwords, if the correction width parameter is “5”, the first thresholdvalue can be equal to 10. However, the first threshold value may be anyother arbitrary value such as a value acquired through an experiment ora measurement in advance. According to this embodiment, if the intervald is equal to or lower than the first threshold value, an equalexposure-amount adjustment parameter is used irrespective of the valueof the interval d. However, if the first threshold value is dt, forexample, exposure-amount adjustment parameters corresponding to intervald=1 through interval d=dt. If interval d≤dt, an exposure-amountadjustment parameter corresponding to the interval d is used. Aninterval d equal to or lower than the first threshold value and anexposure-amount adjustment parameter may be provided in a many-to-oneconfiguration instead of a one-to-one configuration. In other words, aplurality of exposure-amount adjustment parameters may be provided toone interval d equal to lower than the first threshold value.

As illustrated in FIGS. 13A and 13B, the exposure-amount adjustmentparameters are information describing a correction amount for adjustingthe height of toner for an exposure amount, that is, a correction amountfor a pixel value. The exposure intensity in FIGS. 13A and 13B supportsthe method for adjusting an exposure amount based on an exposureintensity as described with reference to FIG. 7B while the PWM supportsthe method for adjusting an exposure amount based on a PWM as describedwith reference to FIG. 7C. According to this embodiment, in a case wherean exposure amount is adjusted on basis of a PWM, the exposure amount isnot corrected for a pixel having toner having a height lower than onedue to an edge effect. In other words, the correction of an exposureamount for a pixel to be corrected includes no correction as a result.FIG. 14A illustrates sub pixels to be exposed of pixels having a pixelvalue equal to “255” by distance from an edge in a case where the PWM isused to adjust the exposure amount in accordance with theexposure-amount adjustment parameters illustrated in FIG. 13A. While subpixels to be exposed may be turned on and off as illustrated in FIG.14A, an OFF time periods may be serially provided as illustrated in FIG.14B.

The exposure amount adjusting unit 903 corrects a pixel value (exposureamount) of each pixel to be corrected in accordance with thecorresponding one of the exposure-amount adjustment parametersillustrated in FIGS. 13A and 13B. Then, the image calculating unit 9controls the exposing unit 7 on basis of the corrected pixel value.

The image regions 1801 a to 1801 c illustrated in FIGS. 9A and 9B have alength in the main scanning direction equal to that of the image regions1802 a to 1803 c. Next, a case in which the image regions 1803 a and1803 b have different lengths in the main scanning direction will bedescribed with reference to FIG. 15. Assuming that the correction widthparameter is “5” and X is 10 pixels, the strength of an edge effect on afront side edge of the image region 1803 b will be described below. Anedge effect occurs on the front side edge of the image region 1803 birrespective of the value of d. However, if the interval d is higherthan the first threshold value or 10 pixels, the strength of the edgeeffect on the front side edge may be equal to that in FIG. 9A at allpixels in the main scanning direction. However, if the interval d isequal to or lower than the first threshold value, the front side edge ofthe image region 1803 b has an weaker edge effect only at pixels in arange Z being an overlapped range in the main scanning direction of theimage regions 1803 a and 1803 b. In other words, five pixels from anedge in the range Z in the main scanning direction have a weaker edgeeffect as in the case in FIG. 9B. On the other hand, five pixels from anedge excluding the range Z in the main scanning direction have an edgeeffect that is not weakened and is substantially equal to that in thecase in FIG. 9A because other pixels to which toner is adhered do notexist within the first threshold value in the sub scanning directionfrom the front side edge.

According to this embodiment, the strength of the edge effect isdetermined on basis of the interval between edges of different imageregions without consideration of the width of the image regions. Inother words, referring to the case in FIG. 15, for example, the strengthof the edge effect occurring at the front side edge of the image region1803 b is determined on basis of the value of d without consideration ofthe value of X. However, the determination of the strength of an edgeeffect may further be based on the value of X. This is because a lowervalue of X means that there is a sufficient amount of toner to besupplied to the image region 1803 b. Therefore, if the value of d isequal to or lower than the first threshold value, the value of X isfurther used for correction of the exposure amount. In this case, asecond threshold value, for example, is defined for the value of X. Anexposure-amount adjustment parameter may be provided in each of caseswhere the value of d is higher than the first threshold value, where thevalue of d is equal to or lower than the first threshold value and thevalue of X is higher than the second threshold value, and where thevalue of d is equal to or lower than the first threshold value and thevalue of X is equal to or lower than the second threshold value. Thesecond threshold value may be 10 pixels, for example, like the firstthreshold value. In a case where the value of d is equal to or lowerthan the first threshold value and the value of X is equal to or lowerthan the second threshold value, a plurality of exposure-amountadjustment parameters corresponding to each of the values of X equal toor lower than the second threshold value may be provided. The value of Xequal to or lower than the second threshold value and theexposure-amount adjustment parameter may be provided in a many-to-oneconfiguration instead of a one-to-one configuration. In other words, aplurality of exposure-amount adjustment parameters may be provided to Xequal to or lower than the second threshold value. Furthermore, aplurality of exposure-amount adjustment parameters may be provided to acombination of the value of d equal to or lower than the first thresholdvalue and the value of X equal to or lower than the second thresholdvalue.

The same processing method as that for an edge in the main scanningdirection may be applied to an edge in the sub scanning direction suchthat the strength of an edge effect is determined and that the exposureamount is adjusted with an exposure-amount adjustment parameter based onthe strength, as described above. Next, a pixel will be described whichpositions within a correction width parameter from an edge in the mainscanning direction and an edge in the sub scanning direction. The pixelmay sometimes be determined as having a stronger edge effect by thedetermination in the main scanning direction and may be determined as aweaker edge effect by the determination in the sub scanning direction.In this case, it may be configured such that the stronger one may beselected. Alternatively, it may be configured such that the weaker onemay be selected.

Next, a method for suppressing an influence of a sweep-up will bedescribed. The same fundamental way of thinking as that for an edgeeffect may be applied to a sweep-up though an edge effect and a sweep-upare different in that an edge effect occurs over a whole edge asdescribed above while a sweep-up occurs at a rear side edge. In otherwords, the fundamental difference is that an edge to be processed is arear side edge. The difference from the processing for an edge effectwill be mainly described below. It is again assumed here that thecorrection width parameter is “5”. FIG. 16A illustrates a height oftoner in a case where a sweep-up occurs in the image regions 1801 a to1801 c in FIG. 9A. The horizontal axis indicates a front side edge as afirst position. Because an interval d1 is equal to 10 pixels that is asufficient width in the image in FIG. 16A, the height of toner on fivepixels corresponding to the correction width parameter from the rear endside edge is high.

On the other hand, FIG. 16B illustrates a height of toner in a casewhere a sweep-up occurs in the image regions 1802 a to 1802 c in FIG.9B. It is assumed here that an interval d2 is equal to one pixel.Referring to FIG. 9B, the sixth pixel, that is, the fifth pixel from therear side edge has a larger height. This is because d2=1 in thisexample. In other words, a sweep-up occurs due to a peripheral speeddifference between the photosensitive member 1 and the developing roller14 as described with reference to FIGS. 5A to 5C. Thus, the pixel havinga sweep-up varies in accordance with the value of the interval d. Morespecifically, when the correction width parameter is y and the intervalis d, the height of the toner between the yth pixel and the (y−d+1)thpixel from the rear end is larger. Therefore, when the interval d ishigher than the correction width parameter, a sweep-up occurs in a rangeto the yth pixel from an edge. The strength of such a sweep-up dependson the interval d, like the edge effect. According to this embodiment,the strength is determined on basis of whether the interval d is largerthan y pixels equal to a third threshold value that is the correctionwidth parameter here. The third threshold value may be another valueacquired through an experiment or a measurement, for example. Like theprocessing for an edge effect, if the interval d is equal to or lowerthan the third threshold value, the strength of a sweep-up may bedetermined in a plurality of steps in accordance with the value of theinterval d. Alternatively, the width in the sub scanning direction of animage region subsequent to the rear side edge may be used for thedetermination of the strength of a sweep-up.

FIG. 17A illustrates pixels identified by the image analyzing unit 901as pixels to be corrected in the image regions 1801 a to 1801 c. Numbers1 through 5 indicate distances (lowest values) from a rear end of anedge. Because the correction width parameter is “5”, the image analyzingunit 901 determines that an edge effect may possibly occur in ranges offive pixels from rear end side edges in the sub scanning direction ofthe image regions 1801 a to 1801 c. FIG. 17B illustrates pixelsidentified by the image analyzing unit 901 as pixels to be corrected inthe image regions 1802 a to 1802 c. In this example, as described above,because the correction width parameter is “5” and d2=1, a sweep-upoccurs at the fifth pixel from the rear end edge, and the strength ishigher than that in the image region 1801 a, which is indicated by “*”.

A pixel influenced by an edge effect or a sweep-up is identified onbasis of a correction width parameter and is determined as a pixel to becorrected. In this case, an interval to a neighboring image region iscalculated, and the exposure-amount adjustment parameter based on thedistance is used. The exposure amount of the identified pixel iscorrected on basis of the distance from the edge. The correction of anexposure amount includes no correction as a result. In other words, apixel to be corrected may be identified, but the exposure amount or thepixel value of the identified pixel may not be changed in accordancewith some exposure-amount adjustment parameters. For example, when thecorrection width parameter is “5”, five pixels from an edge aretypically identified as pixels to be corrected, but the exposure amountof a pixel at a certain distance therefrom may not be changed inaccordance with some exposure-amount adjustment parameters. This isbecause the correction width parameters may be complicated when theexposure amounts of pixels to be corrected are always to be adjusted.With this configuration, the exposure amounts of pixels to which toneris excessively adhered due to an edge effect or a sweep-up can beadjusted. Furthermore, the exposure amounts are not reducedunnecessarily, which can prevent reduction of image quality of an imagein a part adjacent to pixels. Prevention of excessively adhering oftoner can further reduce the consumed amount of toner.

According to this embodiment, all of pixel values of the image regions1801 a to 1801 c, and 1802 a to 1802 c are “255”. However, a pixel witha pixel value equal to or higher than a predetermined value may bedetermined as a black pixel, and a pixel with a pixel value lower thanthe predetermined value may be determined as a white pixel. A regionhaving black pixels continuously may be handled as one image region, anda region having white pixels continuously may be handled as one marginregion.

Second Embodiment

According to the first embodiment, if the interval between image regionsis equal to or lower than the first threshold value, the pixel valuesare adjusted by using an exposure-amount adjustment parameter accordingto the interval because a weaker edge effect or sweep-up effect occurscompared with a case with an interval higher than the first thresholdvalue. However, according to a second embodiment, if the intervalbetween image regions is equal to or lower than a first threshold value,it is determined that no edge effect or sweep-up occurs so that theexposure amount is not adjusted by using an exposure-amount adjustmentparameter. Pixels within a correction width parameter from a pluralityof edges are determined in different directions, and the correspondingexposure amount may be corrected based on the strongest edge effect, forexample.

The aforementioned embodiments apply the image forming apparatus 101.However, the embodiments may be implemented by an image processingapparatus which supplies corrected image data to an image formingapparatus. The image processing apparatus has the image calculating unit9 illustrated in FIG. 1 and generates image data corrected by adjustingthe corresponding exposure amount as described above. The imageprocessing apparatus supplies the generated image data to the imageforming apparatus instead of the exposing unit 7.

Conclusion

The image analyzing unit 901, as described above, identifies a firstregion that is a region serially having pixels having a series of pixelvalues equal to higher than a predetermined value and a second regionthat is a region having a series of pixels having pixel values lowerthan the predetermined value on basis of image data. For example, thepredetermined value may be “1”, and a region having a series of pixelsto which toner is adhered as described in image data may be the firstregion, and a region having a series of pixels to which toner is notadhered as described in image data may be a second region. The imageanalyzing unit 901 identifies pixels to be corrected from pixels withinthe first region based on a correction width parameter beingidentification information regarding a pixel to be corrected. Thecorrection width parameter is information describing a relationshipbetween an edge pixel positioned at an edge of the first region and apixel to be corrected with respect to the edge pixel. For example, foran edge effect, the correction width parameter is information describinga distance from an edge pixel in the sub scanning direction and the mainscanning direction, and a pixel within the distance is a pixel to becorrected. For example, for a sweep-up, the correction width parameteris information describing a distance in the sub scanning direction froman edge pixel on a rear end side in a rotational direction of thephotosensitive member, and a pixel within the distance is a pixel to becorrected.

The exposure amount adjusting unit 903 determines whether any otherfirst region exists which faces the edge pixel across the second regionon a line in a predetermined direction passing through the edge pixel ornot. If another first region exists, the exposure amount of a pixel tobe corrected, which is identified based on the edge pixel and thecorrection width parameter, is corrected by using a first number ofpixels being a number of pixels on the line in the second region betweenthe first region and the other first region. The first number of pixelscorresponds to the interval d according to the aforementionedembodiments. The exposure amount adjusting unit 903 holds firstinformation describing a correction amount applied in a case where thefirst number of pixels is higher than a first threshold value and secondinformation describing a correction amount applied in a case where thefirst number of pixels is equal to or lower than the first thresholdvalue. According to the aforementioned embodiments, the firstinformation and the second information correspond to the exposure-amountadjustment parameters. The exposure amount adjusting unit 903 correctsan exposure amount by using the first information or second informationselected in accordance with the first number of pixels. Theexposure-amount adjustment parameters corresponding to the secondinformation may be provided to a plurality of values of the first numberof pixels equal to or lower than the first threshold value. If the firstnumber of pixels is equal to or lower than the first threshold value,the exposure amount of a pixel to be corrected, which is identified onbasis of the edge pixel and the correction width parameter may not becorrected.

Furthermore, if another first region facing the edge pixel across thesecond region exists on the line in the predetermined direction passingthrough the edge pixel of the first region, the exposure amountadjusting unit 903 determines that second number of pixels being thenumber of pixels on the line in the other first region. Morespecifically, the number of a series of pixels in the other first regionfrom the pixel in the other first region be in contact with the secondregion is determined as a second number of pixels. The second number ofpixels may be used for correcting the exposure amount of the pixel to becorrected, which is identified on basis of the edge pixel and thecorrection width parameter. The second number of pixels corresponds to“X” in FIG. 15 according to the aforementioned embodiments. Thepredetermined direction is the same as the direction in which a pixel tobe corrected on basis of the correction width parameter. In other words,it may be the main scanning direction or the sub scanning direction, orthe main scanning direction and the sub scanning direction. However,other direction may be applicable.

Other Embodiments

The disclosure may be implemented by processing including supplying aprogram implementing one or more functions of the aforementionedembodiments to a system or an apparatus over a network or a through astorage medium and causing one or more processors in a computer in thesystem or apparatus to read and execute the program. The embodiments mayfurther be implemented by a circuit (such as an ASIC) configured toimplement one or more functions.

According to the embodiments, reduction of image quality can besuppressed, and the consumed amount of a developing agent can bereduced.

While the disclosure has been described with reference to exemplaryembodiments, it is to be understood that the disclosure is not limitedto the disclosed exemplary embodiments. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

What is claimed is:
 1. An image forming apparatus forming an image on basis of image data, the apparatus comprising: a photosensitive member; an exposing unit configured to expose the photosensitive member to light to form an electrostatic latent image; a developing unit configured to develop the electrostatic latent image by using a developing agent to form an image; a discriminating unit configured to, on basis of the image data, discriminate a first region being a region having a series of pixels with a pixel value equal to or higher than a predetermined value and a second region being a region having a series of pixels with a pixel value lower than the predetermined value; an identifying unit configured to identify a pixel to be corrected from the pixels within the first region on basis of identification information describing a relationship between an edge pixel positioned at an edge of the first region and the pixel to be corrected; and a correcting unit configured to correct an exposure amount applied by the exposing unit for the pixel to be corrected from an exposure amount described in the image data, wherein, in a case where another first region exists which faces the edge pixel across the second region on a line in a predetermined direction passing through the edge pixel of the first region, the correcting unit determines, in accordance with a first number of pixels being a number of pixels on the line within the second region between the first region and the other first region, whether to correct the exposure amount for the pixel to be corrected.
 2. The image forming apparatus according to claim 1, wherein the correcting unit corrects the exposure amount for the pixel to be corrected in a case where the first number of pixels is higher than a first threshold value and does not correct the exposure amount of the pixel to be corrected in a case where the first number of pixels is equal to or lower than the first threshold value.
 3. The image forming apparatus according to claim 1, wherein, in a case where another first region exists which faces the edge pixel across a second region on a line in a predetermined direction passing through the edge pixel of the first region, the correcting unit corrects the exposure amount of a pixel to be corrected identified on basis of the edge pixel and the identification information further in accordance with a second number of pixels being a number of a series of pixels in the other first region from a pixel within the other first region in contact with the second region on the line.
 4. The image forming apparatus according to claim 1, wherein the predetermined direction is a main scanning direction or a sub scanning direction.
 5. The image forming apparatus according to claim 4, wherein the identification information is information describing a range of pixels to be corrected in the predetermined direction from the edge pixel of the first region.
 6. The image forming apparatus according to claim 1, wherein the predetermined direction is a sub scanning direction; and wherein the identification information is information describing a range of pixels to be corrected in the predetermined direction from the edge pixel of the first region on an upstream side in a rotational direction of the photosensitive member.
 7. The image forming apparatus according to claim 4, wherein the identifying unit does not identify a pixel to be corrected based on the edge pixel in a case where the number of a series of pixels of the first region from the edge pixel is equal to or lower than a predetermined value on the line in the predetermined direction passing through the edge pixel of the first region.
 8. The image forming apparatus according to claim 6, wherein the identifying unit does not identify a pixel to be corrected based on the edge pixel in a case where the number of a series of pixels of the first region from the edge pixel is equal to or lower than a predetermined value on the line in the predetermined direction passing through the edge pixel of the first region.
 9. The image forming apparatus according to claim 1, wherein a pixel with a pixel value equal to or higher than the predetermined value is a pixel to which toner is to be adhered, and a pixel with a pixel value lower than the predetermined value is a pixel to which toner is not to be adhered.
 10. An image processing apparatus supplying output image data for forming an image to an image forming apparatus having a photosensitive member, an exposing unit configured to expose the photosensitive member to light to form an electrostatic latent image, and a developing unit configured to develop the electrostatic latent image by using a developing agent to form an image, the image processing apparatus comprising: a discriminating unit configured to, on basis of input image data, discriminate a first region being a region having a series of pixels with a pixel value equal to or higher than a predetermined value and a second region being a region having a series of pixels with a pixel value lower than the predetermined value; an identifying unit configured to identify a pixel to be corrected from the pixels within the first region on basis of identification information describing a relationship between an edge pixel positioned at an edge of the first region and the pixel to be corrected; and a correcting unit configured to correct an exposure amount applied by the exposing unit for the pixel to be corrected from an exposure amount described in the image data to generate the output image data, wherein, in a case where another first region exists which faces the edge pixel across the second region on a line in a predetermined direction passing through the edge pixel of the first region, the correcting unit determines, in accordance with a first number of pixels being a number of pixels on the line within the second region between the first region and the other first region, whether to correct the exposure amount for the pixel to be corrected. 